This invention relates to a non-fiberglass sound absorbing moldable thermoplastic structure and a method of manufacture, and more particularly to moldable headliners made from such structures for use in motor vehicles.
Prior art constructions of moldable headliners for trucks and automotive vehicles generally included a phenolic saturated fiberglass mat molded into a shell. In a secondary step, a cloth decorative outer layer, usually of a nylon tricot fabric backed with a 3 mm foam layer is attached to the shell. The foam helps to hide imperfections in the fiberglass shell.
The automotive industry recently has moved away from this construction to accepted European technology. This newer technology involves use of a multi-layered composite including a foam core and two outer layers of chopped fiberglass. The fiberglass is either chopped in place or provided in mat form and generally includes fiberglass yarns in tow form cut to about 1.27 to 10.16 cm (1/2" to 4") long. This tri-laminate is saturated with an isocyanate resin which bonds the layers together during the molding process which forms the part into a shape to fit into a specific vehicle. The fiberglass layers on either side of the foam core are included to impart proper stiffness to the headliner part.
The European triplex construction is generally further sandwiched between outer film layers. These film layers act as barriers to prevent the liquid isocyanate resin from penetrating through the top layer which is the decorative fabric . Similarly, the film layer on the back of the part prevents the isocyanate from penetrating the backing mold release layer and contaminating the mold. If the liquid adhesive bleeds through the decorative fabric, it would be visible and a cause for rejection of the part, or it could cause sticking or attachment of the back side of the part to the mold.
There are ongoing efforts in the automotive industry to provide a moldable headliner part which does not include any fiberglass in the construction. This move away from the use of fiberglass is driven by health concerns and/or irritation to workers handling conventional headliners containing chopped fiberglass. The industry also desires to produce a headliner part which can more readily be recycled into a single feed stream. The use of natural fibers such as jute, hemp or flax are other alternatives to fiberglass, but they interfere with recycling into a single feed stream when thermoplastic fibers and/or binders are utilized in other layers of the composite.
One example of a commercial sound absorbing laminate is shown in U.S. Pat. No. 4,828,910 to Haussling. Here the laminate structure includes a reinforcing porous mat of chopped glass fiber integrally bonded to a resilient fibrous batt. A decorative cover sheet covers the exposed or exterior surface of the reinforcing mat all bonded together by a thermoset resin binder. The reinforcing mats sandwiching the fibrous batt are of glass fibers bonded together by a thermoformable resin. Finally, a porous cloth scrim as a release layer is adhesively secured to the back of the reinforcing mat by the thermoset resin coating the mat.
Another type of molded automobile headliner is shown in U.S. Pat. No. 4,840,832 to Weinle, et al. Here, the headliner is formed from a batt of polymeric fibers including at least a portion of potentially adhesive fibers. The headliner is characterized by being of a highly deformable resilient construction to facilitate installation in the vehicle. The fibers in the batt are bonded together at a multiplicity of locations which impart a self-supporting molded rigidity allowing the headliner to retain its shape when installed. A flexible foam layer is adhered to one surface of the flexible batt and the outer textile fabric is bonded to the foam layer.
U.S. Pat. No. 5,591,289 to Souders, et al describes another headliner based on a fibrous batt including binder fibers coated with a thermoset resin for imparting stiffness to the part. In U.S. Pat. No. 5,660,908 to Kelman, et al. A 100% polyethylene terephthalate (PET) headliner is formed from a fibrous batt having a plurality of impressions which are filled with PET filler and bonded to a PET scrim for imparting additional stiffness.
While the constructions using fibrous batts produce some improvement, the weight necessary to achieve the required stiffness is prohibitive. Accordingly, it remains desirable to improve these new constructions and provide a moldable headliner which will absorb sound and which is based on an easily fabricated all thermoplastic materials and wholly non-fiberglass containing moldable structure.